Most Russian pressure vessels can be designed to ASME, providing they have a) Passport, b) Gost R certificate C)GTTN Permit all of which invole a paper chase and a cost. Pepole like SGS can advise cost's for the papper chase. The only point on design/materials would be impact requiments normally...
Know problem in constructing thick walled pressure vessels, would suggest you look closley at materials in soild stainless the cost will be high. If your process/contents of vessel allows why not use carbon steel clad with 3 mm stainless steel this would reduce cost and give you a wall thickness...
My problem /question, vessel inside diameter 84", 2:1 dished head, outlet nozzle required in top head which has an i/d of 48", with reniforcment nozzle o/d 68". Alougth acceptable to code & calc's the head is left with knuckle area only.
Alternative hemi head or cone with 30...